1. Field of the Invention
The present invention generally relates to a seismic load transmitting system for multi-span continuous bridges, and more particularly, to a seismic load transmitting system based on impact mechanism for multi-span continuous bridges, which can improve earthquake resistance capacity of a bridge by transmitting seismic load from the superstructure not only to fixed support piers of the bridge, but also to movable support piers of the bridge.
2. Description of the Related Art
Recently, multi-span continuous bridges are widely used. In general, such a multi-span continuous bridge is designed to have a single fixed point in the longitudinal direction of the bridge. FIG. 6a shows an example of the conventional multi-span continuous bridge. In the conventional 4-span continuous bridge, a fixed support 121 is installed on a fixed support pier 120, which is located in the middle of the 4-span continuous bridge, to restrict the longitudinal movement of the 20 superstructure 100 of the bridge. Movable supports 122 are installed on movable support piers 110 and 130 to permit free longitudinal movement of the superstructure 100 of the bridge. FIG. 6b is a schematic view illustrating the deformation of the 4-span continuous bridge of FIG. 6a when a seismic load is imparted thereto. Referring to FIG. 6b, the seismic load is applied to the superstructure 100 of the bridge in the arrow direction xe2x80x9cbxe2x80x9d by an earthquake ground motion expressed in the arrow direction xe2x80x9caxe2x80x9d. The superstructure 100 of the bridge moves in the longitudinal direction of the bridge due to the seismic load. With no frictional force of the movable supports, the seismic load imparted to the superstructure 100 of the bridge would be transmitted only to the fixed support pier 120 through the fixed support 121. The fixed support pier 120 provided with the fixed support 121 would withstand the whole seismic load transmitted from the superstructure 100 of the bridge, and finally be forced to deform as shown FIG. 6b. If an excessive seismic load is applied to the fixed support pier 120, the bridge itself as well as the fixed support 121 of the fixed support pier 120 would be seriously damaged, maybe resulting in the failure of the fixed support pier 120.
Seismic isolators, i.e., lead rubber bearings, friction pendulum seismic isolation bearings, etc., are conventionally employed to reduce the seismic load transmitted from the superstructure of the bridge to the piers. It is most convenient if the conventional seismic isolators are installed between the piers and the superstructure from the beginning of the construction of the bridge.
Meanwhile, shock transmitters have been developed to transmit the seismic load not only to the fixed support piers but also to the movable support piers by the aid of high viscosity fluid. To be specific, the apparatus is characterized by a cylinder and rods connecting both ends of the cylinder to the superstructure of the bridge and to the piers. In general the cylinder is divided into two chambers by a sliding piston. The chambers are filled with fluid and connected through an orifice. It allows slow displacement under static load such as temperature load. But it provides temporary restraint under the suddenly applied dynamic load such as earthquakes. This apparatus using viscous fluid, however, should always be kept sealed so as to prevent the fluid from leaking out and the function thereof from deteriorating due to the leakage. For this, the apparatus may need measures for continuous monitoring, maintenance and repair. Further, there may be deterioration in the viscosity of the fluid with the passage of time, possibly inducing loss in efficiency of the impact transmitting apparatus and in earthquake resistance capacity of the bridge.
It is, therefore, an object of the present invention to provide a seismic load transmitting system based on impact mechanism for a multi-span continuous bridge, which can overcome the disadvantages of the conventional shock transmitters in a mechanical manner in contrast to the conventional seismic isolator.
To achieve the above object, there is provided a seismic load transmitting system based on impact mechanism for a multi-span continuous bridge, which improves its resistance capacity against earthquakes by converting the seismic load transmitted from a superstructure of the bridge into a compressive force and transmitting the same not only to fixed support piers but also to movable support piers.
To be specific, the seismic load transmitting system comprises impact assemblies (or impactors) that are connected to a superstructure of the bridge for colliding with the movable support piers according to longitudinal displacement of the superstructure of the bridge caused by the seismic load and that transmit the seismic load from the superstructure of the bridge to the movable support piers; and impact receiving assemblies (or targets) that are installed in the movable support piers for receiving impact forces generated when the movable support piers collide with the impact assemblies (or impactors) and that transmit the seismic load from the superstructure of the bridge through the impact assemblies to the movable support piers, whereby the seismic load transmitting system can improve the earthquake resistance capacity of the bridge by converting the seismic load generated in the superstructure due to the earthquake into compressive forces due to the collision between the impact assemblies and impact receiving assemblies and transmitting the seismic load to the fixed support piers but also to the movable support piers.
The seismic load transmitting system according to the present invention has also functions of distributing and transmitting impact forces generated at expansion joints of bridge superstructures owing to the causes other than earthquakes.
According to the present invention, the impact assembly includes a main body, said main body being fixed to the superstructure of the bridge at one end thereof and extending toward the impact receiving assembly at the other end thereof, an impact plate being installed at an end of the main body and facing the impact receiving assembly with a predetermined gap therebetween; and a buffer plate made of an elastic material, the buffer plate being provided in front of the end of the impact plate, for reducing impact load generated when the impact assembly is collided with the impact receiving assembly.
The impact receiving assembly may include a base plate attached to the movable support piers for fixing the impact receiving assembly to the movable support piers, a contact plate being in contact with the buffer plate during the collision between the impact assembly and the impact receiving assembly, and an impact absorbing plate being installed between the contact plate and the base pate to absorb the impact force generated during the collision between the impact assembly and the impact receiving assembly.
The impact assembly may further include a plurality of supplemental intermediate metal plates of a predetermined thickness between the impact plate and the rear of the buffer plate, and the contact plate of the impact receiving assembly has a curved surface of predetermined single or double curvature. The surface of double curvature means a curved surface that is defined by horizontal curvature and vertical curvature that can be different from each other.
In the other embodiment, the impact plate, intermediate plates and buffer plate of the impact assembly have curved surfaces of predetermined single or double curvature.
The impact receiving assembly may further comprise an impact absorbing plate being installed between the contact plate and the base plate to absorb the impact force generated during the collision between the impact assembly and impact receiving assembly.
The contact plate in the impact receiving assembly and the buffer plate in the impact assembly may have, respectively, a curved surface of single or double curvature.
The structures of the impact assembly and the impact receiving assembly can be interchanged each other to achieve the functions intended by the seismic load transmitting system of the present invention.
The impact assembly and the impact receiving assembly may be enclosed by a flexible protection hood, respectively. A shear key may be installed at the upper part of the movable support piers, and the impact receiving assemblies may be installed at both sides of the shear key.